Danny Welbeck came off the bench to wrap up the points in stoppage-time.

Emery was relieved to see Arsenal finally get points on the board, but their inconsistent performance suggests the former Paris Saint Germain boss still has much to work on as he aims to restore his new club to the top four after last season's sixth place finish.

West Ham's third successive defeat under new manager Manuel Pellegrini makes it the worst start by a Hammers boss since Avram Grant lost his opening four league games of the 2010-11 season.

Pellegrini's side sit bottom of the table and have only themselves to blame after wasting several chances to seize control.

Arsenal were without Mesut Ozil, who was reported to be suffering from the flu after missing training on Friday, but the German midfielder's absence couldn't be blamed for his team's erratic efforts at the back.

There was an early warning for the creaky Arsenal defence as Hammers captain Arnautovic fired into the side-netting.

Pellegrini's men snatched the lead with a 25th minute goal that showed Emery hasn't curled the defensive woes that ailed Arsenal in last years of the Wenger era.

When Felipe Anderson took possession in midfield, he was able to advanced unchecked towards the Arsenal penalty area, where he fed a pass into Arnautovic.

Aided by the lethargic reaction of Arsenal defenders Shkodran Mustafi and Sokratis Papastathopoulos, Arnautovic had time and space to drill a low drive past Petr Cech from the edge of the area.

- Revitalised -

Jolted into action by that shock setback, Arsenal were level within five minutes.

Hector Bellerin's dashes forward from right-back were causing West Ham defender Arthur Masuaku all kinds of problems and the Spaniard was the catalyst for Arsenal's equaliser an the climax of a fine 17-pass move.

Breaking onto Henrikh Mkhitaryan's pass down the right flank, Bellerin whipped over a cross that ran through to Monreal at the far post, where the left-back lashed home from close-range.

Emery admitted this week that Pierre-Emerick Aubameyang has been suffering from a confidence crisis after the Arsenal striker failed to score in the opening two games.

Aubameyang was subdued again, the Gabon international threatening just once from long-range, and when Alexandre Lacazette came on to play alongside at half-time, the French forward immediately looked more dangerous than his team-mate.

Benefitting from more astonishingly slack defending, Robert Snodgrass should have put West Ham ahead when he ran clear on goal, but the midfielder let Arsenal off the hook with a tame effort.

Crucially, Arnautovic squandered two chances to restore West Ham's lead with sloppy finishes early in the second half.

Lacazette's introduction had revitalised Arsenal and he drew a good stop from Lukasz Fabianski with a stinging strike.

Arsenal's pressure was rewarded in the 70th minute when Lacazette controlled well on his chest and swivelled for a shot that cannoned off Diop and into his own net.

Arsenal finished well on top and Welbeck tapped in from Bellerin's pass with the Hammers defence in tatters.